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17
Shantz D edzcatzon
Realizing that half of the world's vegetation is of this type, the
potentialities of such an arboretum we are dedicating today become evident. Here can be grown the plants of our own Southwest,
much of Mexico, the desert regions of Chile and Patagonia, the
Great Sandy, the Gibson, the great Victoria deserts of Australia,
the Namib, the Big and Little Karroo, the Karroo Plateau and the
Kalahari, the Sahara, the Libian Desert, the Nubian Desert, SoDr. Homer L. Shantz
mali Land, East African Deserts and the Deserts of Arabia, Persia,
President, University of Arizona
Turkestan, East Turkestan, and Mongolia. Here can be grown the
Tucson Arizona
wonderful varied forms of Cactaceae, a succulent group which
is naturally at home in this section. Here also can be grown the
If the great physiographic divisions are exampled, the earth's sur- equally interesting and varied Euphorbiaceae. A collection of each
face is more distinctly marked by the vegetation cover than by of these groups would be a notable achievement and probably no
any other feature. The land area of the world amounts to about garden could be better located for this purpose. The Mesembryan52,000,000 square miles. Of this area, less than 25,000,000 square themums of South Africa would rank second in interest to no other
miles of forest and grassland are climatically suited to produce group. Here could be collected most of the Acacias, of Africa,
crops without irrigation. This more humid area may be divided Asia, Australia, and America, a wonderful group judged either as
on the basis of temperature into a tropical area covering about ornamental, or as trees productive of gums, tannin, wood and for12,800,000 square miles and a temperate area covering about age; the Combretums, equally interesting and hardly known in our
11,500,000 square miles. In this latter division, about 3,000,000 plantings; great groups such as the Yuccas, Agaves, Aloes, Cotylesquare miles are grassland, 7,600,000 square miles are coniferous dons and the various other succulents, not to mention the wealth
forest land, and 6,500,000 square miles are deciduous forest land. of shrubbery and bulbous plants limited only to this dry country.
This deciduous forest land, the home of our race until less than a Probably more species can be grown here at this Arboretum under
century ago, is located in western Europe, eastern Asia, and the natural conditions than under the same conditions in all of the gareastern part of the United States. In this area are located, with few dens of eastern United States and Europe.
exceptions, that botanical gardens and arboreta of the world. Climatically, these gardens are adapted to grow plants from only one- With the addition of a little irrigation, the scope may be extendeighth or less than twelve· percent of the land area of the world. ed over another 1,200,000 square miles of sclerophyll forest and
Here are located such great botanical gardens as the Missouri Bo- brushland, the Mediterranean flora, the Cape flora, areas in Chile
tanical Garden, the new National Arboretum at Washington, the and Australia, and the southwestern part of the United States. The
Brooklyn Botanic Garden and hundreds of lesser gardens in the potentialities are entirely beyond the possibilities of realization,
United States. The great gardens of Europe, such as the Kew Gar- even if the Arboretum had limitless funds, but it may and should
dens of London, the Gardens of Berlin and Paris and many other become one of the world's most noted gardens, for the physical
European cities, are all located in the deciduous forest area. The plant is here, and the areas of exploration are great and interesting.
restricted natural environment of these great gardens is supple- Compare this opportunity with that afforded by the other arboreta
mented by greenhouses in which many plants are grown under of the world and realize that the area to be drawn upon is at least
World Vegetation in Relation
to the Boyce Thompson
Southwestern Arboretum
glass. Plants from the other seven-eighths of the world area are
grown with great difficulty and often scarcely resemble the same
species in its native habitat. In this deciduous forest area are concentrated the botanical gardens of the world, and, while there are
none too many gardens in this area, the proportion in other parts of
the world is lamentably small.
Half the land area of the world, or 26,000,000 square miles, characterized by desert savanna and desert shrubs, is too dry to produce
ordinary crops and mesophytic plants without irrigation. This area
is desert or semi-desert in character, where droughts are long and
periods of rainfall short, where plants stand for months without
water available for growth, and where water is the one and often the only limiting factor. Known as a desert country, there are
here found many of the most beautiful plants in all the world and
certainly many of the most interesting. Plant growth in the desert is limited in quantity but not variety. Here only those plants
which have developed every possible protective device of growth
habit, morphological structure, and physiological adjustment can
succeed. The extreme conditions are met by a thousand different
adjustments. This in itself would make the flora of the desert more
interesting than any other type.
four times as great, the number of species probably far greater, and
the extremes of adjustment and variety of form many times as great
as any found in the humid climates. On a small area of the earth's
surface, 6,500,000 square miles, we have concentrated most of our
botanical and horticultural efforts, while half the world's area has
been entirely neglected. It is from this on half of the world's area
that we can draw plants for this Arboretum.
To Colonel Thompson belongs the distinction of having first met
this need and appreciated this great opportunity, of having been
the first to set aside and area for the collection and study of the
plants which have morphologically and physiologically made the
adjustments to extreme conditions. Surely no greater opportunity
ever fell to the lot of any man. This Arboretum, wisely administered and adequately endowed, can contribute to the solution of
the problems of the desert plants and to better understand their
morphology and physiology. It should become a great center for
the study of desert plants and desert problems from both the scientific and the practical sides. We have here an institution that will be
visited and utilized by people all over the world. The opportunity
is a great one, and the establishment of the Arboretum may well
become one of the most important and worthwhile adventures in
plant work undertaken during the last century.